Method for introducing a prestress to a cylindrical concrete structure

ABSTRACT

A method for introducing a prestress to a cylindrical concrete structure is disclosed, which is characterized by the steps of providing a desired number of step portions or notched portions having outer peripheral inclined faces, the thickness of which vary gradually either in the direction of generating lines of the cylinder structure or in the circumferential direction thereof, respectively. The inclined faces extend either along the circumferential direction or along the direction of the generating lines on the outer peripheral surface of the cylindrical structure. Wedge members are slidably disposed on the respective inclined faces and also jacks are provided for sliding the wedge members. Tensioning members are wound around the outer peripheral surfaces of the wedge members along the circumferential direction. The tensioning members wound around the outer periphery of the inclined faces in the circumferential direction are tensioned by operating the jacks to cause the respective wedge members to slide along the inclined faces; whereby a prestress is introduced to the cylindrical concrete structure.

United States Patent 91 Hiraga [111 3,711,935 51 Jan. 23, 1973 METHOD FOR INTRODUCING A PRESTRESS TO A CYLINDRICAL CONCRETE STRUCTURE [75] Inventor: Ken-[chi Hiraga, Tokyo, Japan [73] Assignee: Taiser Kensetsu Kabushiki Kaisha,

Tokyo, Japan 22 Filed: 01.1.21, 1970 21 Appl.No.: 82,581

[30] Foreign Application Priority Data Sept. 15, 1970 Great Britain ..44,093/70 [52] US. Cl ..29/452 [51] Int. Cl. ..Bzld 39/00 [58] Field of Search ..29/452, 155, 424; 52/224; 254/29 A [56] References Cited UNITED STATES PATENTS 2,597,084 5/1952 Huddleston ..52/224 X 3,278,128 10/1966 Szulc ...52/224 UX 3,353,859 11/1967 Schupack ..52/224 X 3,552,940 1/1971 Portas et a1 ..29/452 3,568,379 3/1971 Johnson et al ..52/224 X Primary Examiner-Charlie T. Moon Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT A method for introducing a prestress to a cylindrical concrete structure is disclosed, which is characterized by the steps of providing a desired number of step portions or notched portions having outer peripheral inclined faces, the thickness of which vary gradually either in the direction of generating lines of the cylinder structure or in the circumferential direction thereof, respectively. The inclined faces extend either along the circumferential direction or along the direction of the generating lines on the outer I peripheral surface of the cylindrical structure. Wedge members are slidably disposed on the respective inclined faces and also jacks are provided for sliding the wedge members. Tensioning members are wound around the outer peripheral surfaces of the wedge members along the circumferential direction. The tensioning members wound around the outer periphery of the inclined faces in the circumferential direction are tensioned by operating the jacks to cause the respective wedge members to slide along the inclined faces; whereby a prestress is introduced to the cylindrical concrete structure.

10 Claims, 13 Drawing Figures PATENTEDmzs I975 3.711.935

sum 1 0F 4 1:. QKIZQZLZTQ:

KEN-ICHI HIRAGA,

INVENTOR ATTORNEY s PATENTED JAN 23 1975 SHEET 2 OF 4 ATTORNEY 5 PATENTEUJAN 23 1975 SHEET 3 0F 4 FIG. 7

KEN-ICHI HIRAGA,

I NV ENTOR ATTORNEY PATENTED JAN 2 3 I975 SHEET UF 4 FIG. ll

FIG. IO

FIG. I?)

KEN-ICHI HIRAGA INVENT OR ATTORNEY METHOD FOR INTRODUCING A PRESTRESS TO A CYLINDRICAL CONCRETE STRUCTURE The present invention relates to a method for introducing a prestress to a huge cylindrical structure such as, for example, a pressured vessel of atomic piles or the like, a water tank, a water tower, etc.

One of the principal objects of the present invention is to provide an improved method for insuring the introduction of a desired prestress to a cylindrical concrete structure by means of a simple operation.

Another principal object of the present invention is to provide an improved method for introducing a desired prestress to a cylindrical concrete structure by making use of a very small jacking force.

Still another principal object of the present invention is to provide an improved method accompanied with little loss of tension in the tensioning members for introducing a prestress to a cylindrical concrete structure.

Yet another principal object of the present invention is to provide an improved method wherein the tensioning members for introducing a prestress to a cylindrical concrete structure are not apt to be subjected to a deteriorative effect due to the temperature and/or the radiation rays within said structure.

In order to achieve the aforementioned various objects, the method of the present invention is characterized by the steps of providing a desired number of step portions or notched portions having outer peripheral inclined faces, the thickness of which vary gradually either in the direction of generating lines or in the circumferential direction, respectively of the cylindrical structure, and which extend along either the circumferential direction on along the direction of the generating lines on the outer peripheral surface of the cylindrical structure. Wedge members are slidably disposed on the respective inclined faces also jacks also are positioned for sliding the wedge members. Tensioning members are wound around the outer peripheral surfaces of the wedge members along the circumferential direction. The tensioning members are stretched around the outer periphery of the inclined faces in the circumferential direction, by operating the jacks to cause the respective wedge members to slide along the inclined faces; whereby a prestress may be introduced into the cylindrical concrete structure.

As described, according to the present invention, since the outer peripheral surfaces of the desired number of step portions or notched portions provided either along the circumferential direction or along the direction of generating lines on the outer periphery of the cylindrical concrete structure to which a prestress is to be introduced are formed of inclined faces, where the thickness varies gradually either in the direction of generating lines or in the circumferential direction, respectively, of said structure; and since after the tensioning members for introducing a prestress have been circularly wound around the outer peripheral surfaces of the wedge members slidably provided on the inclined faces, the wedge members are caused to slide along the inclined faces by means of the jacks. The peripheral lengths of the circular tensioning members are caused to increase, resulting in stretching in the circumferential direction of the tensioning members; whereby the stretching force may be introduced as a compression prestress to the cylindrical concrete structure via the wedge members,

Therefore, according to the present invention, upon stretching tensioning members for introducing a prestress to a cylindrical concrete structure, it is only necessary to displace the wedge members on which the tensioning members are wound by means of the jacks without directly stretching the tensioning members by making use of jacks, so that a desired large prestress can be introduced into the cylindrical concrete struc ture with an extremely small jacking force, and also a large stretching force is not required in the step of winding the tensioning members around the wedge members but instead the necessary work can be carried out simply. Still further, since the tensioning members make contact only with the outer peripheral surfaces of the wedge members and are in a free state, there occurs no loss of stretching force due to frictional resistance upon stretching the tensioning members.

In addition, according to the present invention, since the tensioning members do not penetrate through the inside of the wall member of the cylindrical concrete structure but are positioned along the outer peripheral surface of the wall member, the arrangement of the tensioning members does not prevent the construction work for the concrete body of the structure and does not lower the efficiency of construction. Also since the strain of the tensioning members can be directly measured, the control of the tension may be carried out securely, refastening of the tensioning members may be readily achieved if necessary. Further, by winding the tensioning members in a number of overlapped layers, a large prestress can be applied, and when the present invention has been applied to an atomic pile, the tensioning members are less apt to be subjected to a deteriorative effect of its internal temperature and/or radiation rays than in the case of positioning within the wall member.

Other advantages and features of the present invention will become more apparent from the following description of the invention in connection to its preferred embodiments illustrated in the drawings, in which:

FIGS. 1 and 2 are perspective view, and a partial enlarged longitudinal cross-section view, respectively, of a cylindrical concrete structure to which the present invention is applicable,

FIG. 3 is a partial longitudinal cross-section elevation view showing a working state according to one preferred embodiment of the present invention,

FIG. 4 is a longitudinal cross-section view showing a working state at the upper end portion of the structure,

FIG. 5 is a longitudinal cross-section view showing a working state according to another preferred embodiment of the present invention,

FIGS. 6 and 7 are a transverse cross-section view showing a working state according to still another preferred embodiment of the present invention, and a perspective view of a cylindrical structure to which the same method is applicable, respectively,

FIG. 8 is a longitudinal cross-section view showing a working state according to yet another preferred embodiment of the present invention,

FIGS. 9 and 10 are longitudinal cross-section view showing a working state according to still another preferred embodiment of the present invention, and a partial perspective view of a cylindrical concrete structure to which the same method is applicable, respectively,

FIGS. 11 and 12 are a transverse cross-section view and a partial enlarged transverse cross-section view,

= respectively, showing a working state according to yet another embodiment of the present invention, and

FIG. 13 is a perspective view of a cylindrical concrete structure to which the method illustrated in FIGS. 11 and 12 is applicable.

Referring now to the accompanying drawings, FIGS. 1 and 2 illustrate a cylindrical concrete structure (A) to which the method according to the present invention is applicable. On the outer peripheral surface of a cylindrical body (1) having a thickness a and a radius r are provided circular step portions (2) extending along its circumferential direction, at fixed intervals in the direction of generating lines of the cylinder. The outer peripheral inclined faces (2a) of the respective steps (2) are inclined in the direction of generating lines with a gradient of desired angle with respect to the vertical surface, and the lower end faces (2b) are formed at right angles with the inclined faces (2a) of the next succeeding step portion (2).

In this connection, the gradient angle 0 of said step portions (2) is selected depending upon the coefficient of friction of the wedge members as described later, the capability of the jacks, and the radius of said structure. Once the angle 6 is determined, the length b in the direction of generating lines of each step portion (2) is selected so that it may become equal to the sum of the lengths of the jack and the wedge member along each inclined face, the stroke of the jack, and an appropriate additional length, and also so that the length c of the lower end face of the step portion (2) may become longer than a dimension necessary to accommodate the jack.

In addition, at the upper end of said body (1), a step portion (2') directed oppositely to step portions (2) is provided.

Now according to the present invention, as shown in FIG. 3 wedge member (3) is mounted on the inclined face of a first step portion (2) slidably in the upward and downward direction. Between the lower end face (2b) of the step portion (2) just above the first step portion (2) and the upper end face of the wedge member (3) in parallel to said face (2b) is interposed a hydraulic jack (4), which is fixedly secured to the lower end face (2b).

On the outer peripheral surface (3a) of said wedge member (3) in parallel to the outer peripheral surface of the body (1), are provided a number of recessed channels (3b) extending in the circumferential direction, and annular tensioning members (5) are wound around and fitted in the recessed channels (3b) of the respective wedge members (3) mounted on each step portion (2) along the same circumference.

Subsequently, if the jacks are actuated to cause the wedge members (3) to slide downwardly along the inclined face (2a), then the tensioning members (5) are stretched so as to be extended in the circumferential direction, the stretching force being introduced as a compression prestress to the body (1) via the wedge members (3).

At this time, in order to smooth the sliding movement of the wedge member (3) along the inclined face (2a), it is preferable to dispose a metallic plate and/or a lubricant material such as molybdenum dioxide onthe inclined face (2a).

After a desired stretching force has been imposed to the tensioning member (5) as described above, in order to prevent backward movement of the wedge member (3), between the wedge member (3) and the lower end face (2b) of the inclined face (2) is interposed a wedge for preventing sliding movement or a quick setting material such as high-early-strength cement.

After the aforementioned operation has been carried out at a desired step portion, the same operation as the above is carried out at the next succeeding step portion, and subsequently similar operations are repeated to introduce a desired compression prestress to the body (1 In this connection, at the upper end portion of the body (1) a jack (4) is interposed between a pair of wedge members (3), (3) mounted respectively on the oppositely directed inclined faces (2a) and (2a) of the opposed step portions (2'), (2) and wound with the tensioning members (5), respectively, as shown in FIG. 4. Both wedge members (3), (3) are simultaneously cause to slide in the upward and downward directions by jack (4) to impose a stretching force to the respective tensioning members (5), whereby a compression prestress may be introduced to the body (1) via the wedge members (3), (3).

When the introduction of a prestress to the body (1) has been completed as described above, tensioning members (5) are covered with protective mortar, and thereby the entire process has been completed.

FIG. 5 illustrates the case where the outer peripheral wall face (2) of the cylindrical concrete structure (A) is provided so that the outer diameter may gradually increase while going towards the bottom over the entire length in the direction of generating lines, in which case the wedge members (3) wound with annular tensioning members (5) are mounted adjacent to each other in the vertical direction, these wedge members (3) being adapted to be shifted downwardly along the outer peripheral wall surface (2) by means ofjack devices to impose a stretching force to tensioning members (5).

The embodiment in FIG. 6 shows the case where the subject method has been applied to a cylindrical concrete structure (A) such as shown in FIG. 7, in which the step portions extending in the direction of generating lines of the structure are disposed at predetermined intervals along the circumferential direction thereof. Since the operation therefor is substantially the same as the preceding embodiments, a more detailed description will be omitted. In the figure, equivalent components to those of the preceding embodiments are given the same references. When the introduction of a prestress has been finished, tensioning members (5) are covered with protective mortar, and then the entire process has been completed.

FIG. 8 shows the case where the method according to the present invention has been applied to a large thick cylindrical concrete structure, in which case after the innermost first layer body (1A) has been constructed similarly to the preceding embodiments and a compression prestress has been introduced thereto, a

second layer body (113) is constructed on its outer periphery and a prestress is introduced thereto similarly to the preceding embodiments. Subsequently similar operations may be repeated to construct a cylindrical concrete structure having a desired large thickness and having a uniform prestress introduced thereto. In the figure, equivalent components to those of the preceding components are given the same references.

FIGS. 9 and 10 show another embodiment of the present invention, in which among the step portions (2) provided on the outer peripheral surface of the body (1), but the positions of the step portions (2) in the columns adjacent to each other in the circumferential direction are staggered to each other in the direction of generating lines of the structure. This structure is useful for shortening the intervals between adjacent tensioning members (5) in the vertical direction. In the figure, equivalent components to those of the preceding embodiments are given the same references.

FIGS. 11-13 show still another embodiment of the present invention. As shown in FIG. 13, on the outer peripheral surface of the cylindrical body (11) are provided notched portions (12) having a V-shaped crosssection and extending in the direct on of generating lines of the structure at predetermined intervals along the circumferential direction. On the laterally opposed inclined faces (12a), (12b) of respective notched portions (12) are slidably provided wedge members (13), (13) respectively. A jack (14) is interposed between the wedge members, and annular tensioning members (15) are wound around the outer periphery of the respective wedge members (13). The tensioning members (15) are stretched by actuating jack (14) to cause both wedge members (13), (13) to slide along the inclined faces (12a), (12b) in directions opposite to each other, whereby a compression prestress may be introduced to the body (11) via the wedge members (13).

While the present invention has been described above in connection to its preferred embodiments, it is intended that the present invention is, of course, not limited only to such embodiments, but various changes in design and operation could be made within the scope of the invention without departing from the spirit thereof.

What is claimed is:

1. A method for introducing a prestress to a cylindrical concrete structure comprising the steps of providing a plurality of step portions having outer peripheral inclined faces around the periphery of said cylindrical concrete structure; positioning wedge members slidably on said inclined faces; positioning jacks for sliding said wedge members along said inclined faces; winding tensioning members around the outer peripheral surfaces of said wedge members along the circumferential direction of said structure; and stretching said tensioning members in said circumferential direction by operating said jacks to cause said wedge members to slide along said inclined faces; thereby introducing a prestress into said cylindrical concrete structure.

2. A method as claimed in claim 1, wherein said step portions are provided to extend circumferentially of said structure and to have the thickness thereof vary in the longitudinal direction of said structure.

3. A method as claimed in claim 2, wherein said inclined faces are separated by end faces perpendicular to said inclined faces, and said jacks are positioned between said wedge members and said end faces.

4. A method as claimed in claim 2, wherein adjacent of said inclined faces join, and each of said jacks are positioned between a pair of said wedge members.

5. A method as claimed in claim 1, wherein said step portions are provided to extend in the longitudinal direction of said structure and to have the thickness thereof vary in the circumferential direction of said structure.

6. A method as claimed in claim 5, wherein said inclined faces are separated by end faces perpendicular to said inclined faces, and said jacks are positioned between said wedge members and said end faces.

7. A method as claimed in claim 5, wherein adjacent of said inclined faces join, and each of said jacks are positioned between a pair of said wedge members.

8. A method as claimed in claim 1, wherein said step portions are provided to have the thickness thereof vary in the longitudinal direction of said structure, step portions adjacent in the circumferential direction of said structure being staggered in said longitudinal direction.

9. A method as claimed in claim 1, further comprising the step of providing metallic plates on said inclined faces.

10. A method as claimed in claim 1, further comprising the step of providing lubricant material on said inclined faces. 

1. A method for introducing a prestress to a cylindrical concrete structure comprising the steps of providing a plurality of step portions having outer peripheral inclined faces around the periphery of said cylindrical concrete structure; positioning wedge members slidably on said inclined faces; positioning jacks for sliding said wedge members along said inclined faces; winding tensioning members around the outer peripheral surfaces of said wedge members along the circumferential direction of said structure; and stretching said tensioning members in said circumferential direction by operating said jacks to cause said wedge members to slide along said inclined faces; thereby introducing a prestress into said cylindrical concrete structure.
 2. A method as claimed in claim 1, wherein said step portions are provided to extend circumferentially of said structure and to have the thickness thereof vary in the longitudinal direction of said structure.
 3. A method as claimed in claim 2, wherein said inclined faces are separated by end faces perpendicular to said inclined faces, and said jacks are positioned between said wedge members and said end faces.
 4. A method as claimed in claim 2, wherein adjacent of said inclined faces join, and each of said jacks are positioned between a pair of said wedge members.
 5. A method as claimed in claim 1, wherein said step portions are provided to extend in the longitudinal direction of said structure and to have the thickness thereof vary in the circumferential direction of said structure.
 6. A method as claimed in claim 5, wherein said inclined faces are separated by end faces perpendicular to said inclined faces, and said jacks are positioned between said wedge members and said end faces.
 7. A method as claimed in claim 5, wherein adjacent of said inclined faces join, and each of said jacks are positioned between a pair of said wedge members.
 8. A method as claimed in claim 1, wherein said step portions are provided to have the thickness thereof vary in the longitudinal direction of said structure, step portions adjacent in the circumferential direction of said structure being staggered in said longitudinal direction.
 9. A method as claimed in claim 1, further comprising the step of providing metallic plates on said inclined faces.
 10. A method as claimed in claim 1, further comprising the step of providing lubricant material on said inclined faces. 